IL23 is composed of the IL12 p40 subunit and a p19 subunit (IL23P19 or IL23A). The p19 subunit shares sequence similarity with IL6 subfamily members and is distantly related to the p35 subunit of IL12. It shows no biological activity by itself, instead, it combines with the p40 subunit of IL12 to form a biologically active, composite cytokine, IL23. IL12 and IL23 are molecules mainly produced by activated accessory and antigen- presenting cells. Both IL23 and IL12 can activate the transcription activator STAT4. In contrast to IL12, which acts mainly on naive CD4(+) T cells, IL23 preferentially acts on memory CD4(+) T cells. IL12 used to be thought to be the prime-regulator of TH1 development but upon discovery of IL23 and the fact that the large subunit of IL23 is shared by IL12, it is now thought that the features attributed to IL12 and TH1 development in inflammation are, in fact, dependent on IL23 rather than IL12. IL23 is implicated in protective and autoimmune responses.
Alternate names: IL-23 subunit alpha, IL-23p19, Interleukin-23 subunit p19, SGRF